list_identities

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover the read-only/idempotent safety profile, so the bar is lower, yet the description adds substantial context: trustLevel states TRUSTED_VERIFIED, TRUSTED_UNVERIFIED and UNTRUSTED, and notes that UNTRUSTED blocks sending until re-trusted, plus that the tool never mutates trust. That is meaningful behavioral disclosure beyond the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the purpose, then the filter, then the return shape, then the trust semantics and usage trigger. Sentences are dense but every one carries information an agent needs, with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description compensates by enumerating all returned fields (number, uuid, fingerprint, safetyNumber, scannableSafetyNumber, trustLevel, addedTimestamp) and explaining the enum-like trust levels. Nothing needed to call or interpret it is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the single parameter is fully documented there, so baseline 3 applies. The description restates E.164 format and the omit-for-all behavior without adding syntax or format detail beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('List stored Signal identity keys (safety numbers) and their trust levels, from the local store'), immediately distinguishing it from siblings like trust_identity and list_contacts. An agent knows exactly what data comes back without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit triggers ('Use it when Signal reports safety number changed or before trust_identity') and an explicit exclusion of what it does not do ('it does not change trust itself'), which routes the agent to trust_identity for mutations. The 'omit it for all' filtering condition is also spelled out.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.